The present invention relates generally to apparatus for supporting internals such as liquid collectors, liquid distributors, packing supports, and vapor-liquid contact devices in columns in which mass transfer and/or heat exchange processes occur and to methods for assembly of the apparatus.
Various types of internals are used in mass transfer and heat exchange columns to facilitate the desired interaction between fluid streams flowing in countercurrent relationship within the open internal region within the column. The term mass transfer column as used herein is not intended to be limited to columns in which mass transfer is the primary objective of the processing occurring within the column, but is also intended to encompass columns in which heat transfer rather than mass transfer is the primary objective of the processing. The internals used within mass transfer columns include liquid collectors, liquid distributors, packing supports, and trays that extend across the horizontal cross section of the column and are supported on rings, bolting bars or other structures fixed or otherwise secured to the inner surface of the column shell.
In larger diameter columns, supports in the nature of beams and trusses are commonly used to resist the deflection or sagging of the internals that would otherwise result from the weight of the internals and the loads exerted on the internals by the fluid streams. This sagging of the internals is generally undesirable because it causes fluid maldistribution as the fluid stream tends to flow toward and pool at the low portion of the internal rather than flowing in the desired uniform manner across or within the internal. These supports are typically fixed at their opposite ends to the column shell and extend horizontally across the open internal region of the column in parallel, spaced-apart relationship. The internal then rests on a top surface of the supports or on lower flanges provided on the supports.
An opening with a closeable cover, known as a manway, is provided in the shell of the mass transfer column to allow a person to enter the column for installation, inspection and servicing of the column internals. A manway is also used to allow passage of the internals through the column shell during initial installation of the internals and during revamping of the column. The size of the manway dictates the size of the internals that can be passed through the manway. For this reason, the internals are typically fabricated in multiple segments that are each small enough to pass through the manway. The internals are then assembled within the column by bolting or welding the individual segments together. The internals can be disassembled in the reverse operation.
During the initial construction of larger-diameter mass transfer columns, the shell is often assembled in sections, with the internals being easily installed through the open top of the associated shell section without the size constraints presented by the manway. Nonetheless, it may be desirable to assemble the internals for these columns from segments that are sized to fit through the manway to allow the internals to be disassembled and removed from the column during later revamping of the column.
It is generally undesirable to use bolts to secure individual segments of the supports together in larger-diameter mass transfer columns because the high loads carried by the supports may cause enough deflection in the support to expose some bolts to a high enough shear force to cause failure of the bolts. Upon failure of these bolts, a higher shear force is then shifted to other bolts and a progression of bolt failures may occur that could lead to greater deflection and ultimately collapse of the support and the associated internal. Welding the support segments together reduces this risk of deflection and collapse, but welding requires more specialized installation personnel than is required when bolting the segments together. In addition, welding the support segments together may not be an available option within certain columns, such as during a column revamp when the residues from the processing that has occurred in the column present a risk of fire or explosion. A need has thus developed for support segments that can be assembled in a manner that overcomes the problems discussed above.